A system for continuous sampling of bioaerosols generated by a postal sorting machine

by Richardson, Mathews Sears

Abstract (Summary)

In this study, a system for the collection of bioaerosols emitted from the mail sorting process was designed and characterized. Two different wetted-wall cyclones, the JBPDS cyclone and the glass cyclone sampler (GCS), were evaluated as system collection devices. These devices operate at 780 L/min and have a D50 of ~ 1 ?m. A trimming impactor with a D50 of 10 ?m was used upstream of the collection devices. Using two reference probes, the cyclone liquid outputs were compared with aerosol collected on filters and the output of an Aerosol-to-Hydrosol Transfer Stage (AHTS).

The mass emission rate of the postal sorting machine was 3.15 mg/min and found not to vary significantly with flow rates above 700 L/min. On average, greater than 66% of the mass collected had a Da < 10 ?m. Using a Coulter Counter, the volume median diameter (volume equivalent) for both device hydrosol outputs was 4.18 ?m. For the effluent aerosol, the volume median diameter was 12.5 ?m.

For a bioaerosol release, this study found that greater than 65% (by volume) of the material released had a Da greater than 7.2 ?m. Using filters, it was found that on average, 95% of the bioaerosol particles emitted had a Da less than 10 ?m. According to the reference data, the expected number of bioaerosol particles in 1.5

times that collected by the GCS and 5.5 times that collected by the JBPDS cyclone for a one milligram release. The time constant for the system in response to a letter release was found to be 1.3 minutes for the GCS and 1.75 minutes for the JBPDS cyclone.

A final note to this study states that the probe dimensions were incorrectly developed, therefore affecting the aspiration efficiency of the probes. In turn, this may have affected the outcome of some of the results. A plot is given at the end of the paper showing to what extent the results may have been affected. It is recommended that further experimental studies be performed to verify the results in this study.